At present, the grinding plates of vertical roll mills are driven by means of an unregulated asynchronous or synchronous motor and multistage gearing. With this arrangement, in practice very large torque variations arise, induced by the grinding process. Furthermore, an intensification of these torque variations may occur due to the oscillatory drive train (clutch, shafts, components with rigid teeth). A roll mill is known, for example, from DE 36 33 747 A1.
To be able to withstand these alternating high loads, all components directly and/or indirectly involved in the drive path must be designed specifically. In particular the alternating stresses due to characteristic vibrations within the drive train lead to a complex and therefore expensive designs. Moreover, in the case of larger mills, transmission damage has been known to occur which gives rise to severe operating losses on the part of the plant operator and can therefore generate a negative image for these mills.
In addition to the moment fluctuations, variations in the speed of rotation of the grinding plate also occur due to the irregular drive and the presence of elasticities. These are undesirable, as they can disturb the grinding process and in particular the grinding bed, and so negatively influence both throughput performance and energy consumption.
DE 36 40 146 A1 describes a planetary differential gear having a main and an auxiliary drive shaft for generating adjustable speeds of rotation. Via additional gear members, a couplable and decouplable power-transmitting connection may be made between the two drive shafts. DE 35 45 314 C2 discloses gearing for conveyor systems and for recovery or crushing plant, having at least one planetary spur gear stage as the driven stage and a gear wheel input stage connected to the driving motor. A torque-measuring device monitors the torque. If a settable maximum torque is exceeded, the driving motor is switched off.
The underlying aim of the invention is to propose a roll mill and a method of operating the roll mill wherein torque variations of the drive and/or variations in the rotation speed of the grinding plate are damped.